The installation of electrical devices, such as circuit breakers, in switchboard and panelboard apparatus is generally of two types. In one type of installation, circuit breakers are essentially stationarily mounted to structural members or frame of the switchboard, typically with terminal electrical connection effected via bolted joints. Alternatively, circuit breakers may be physically supported solely by the switchboard buswork via these bolted terminal joints. In such stationary installations, inspection and maintenance of the circuit breaker is difficult and quite hazardous if attempted while the switchboard is live. In some situations, the hazards must be assumed, since de-engerization of the switchboard and thus interruption of electrical service to all of the branch circuits in the switchboard cannot be tolerated. To reduce the hazards of working with live switchboards, devices are provided with plug-in or stab-type primary disconnect contacts which do not require the direct contact and manipulation to effect their connection and disconnection with mating disconnect contacts of the switchboard. Thus, the device, e.g., circuit breaker, can be plugged in and unplugged from a live switchboard in relative safety.
In higher current applications, the circuit breakers are physically large and quite heavy, thus rendering the bodily movement of the circuit breaker necessary to electrically connect and disconnect it from the switchboard cumbersome if not impossible, unless mechanical assistance is afforded. Not only does the weight and bulk of the circuit breaker become difficult for the electrician to handle, but, as the current ratings increase, the contact pressures of the primary disconnect contacts become extremely difficult, if not impossible to overcome. To surmount these problems, so-called "drawout" apparatus has been resorted to for both supporting the circuit breaker and affording mechanical assistance in overcoming the extreme contact pressures of the disconnect contacts.
It is a general object of the present invention to provide improved drawout apparatus capable of racking electrical devices of large size and weight in an electrical enclosure.
An additional object of the present invention is to provide drawout apparatus of the above character, which affords enhanced mechanical assistance in achieving engagement and disengagement of the load current carrying primary disconnect contacts having high contact pressures for increased current carrying capacity.
A further object of the invention is to provide drawout apparatus of the above character capable of utilization in enclosures of shallow depths, and yet accomodates movement of the device well out from the enclosure to a fully extended position facilitating mounting and dismounting of the device.
Still another object of the present invention is to provide drawout apparatus of the above character, which incorporates various locking and latching features calculated to insure proper operation by authorized personnel in relative safety.
Yet another object of the present invention is to provide drawout apparatus of the above character, which is inexpensive to manufacture, efficient in design, rugged in construction, and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.